1. Field of the Invention
This invention relates to the field of drug delivery systems for the topical administration of medication, and, more particularly, a topical drug delivery system utilizing a viscoelastic gel pad having a liquid fraction wherein the medication is incorporated within the liquid fraction, and still more particularly, a topical anesthetic delivery system using a viscoelastic gel pad having an alcohol and water liquid fraction wherein a topical anesthetic, such as lidocaine base, is dissolved in the alcohol and water liquid fraction.
2. Description of the Prior Art
The inventor previously has developed a Drug Delivery System For The Removal of Dermal Lesions, for which U.S. Pat. No. 5,167,649 was issued, which utilizes a viscoelastic rubber and oil gel which is partially encapsulated between two layers of oil and water impermeable material, where the skin contacting layer includes an aperture which is smaller than, and located within, the periphery of the pad. In conjunction with further development of pharmacological applications of the invention, it was discovered that the general inventive structure has additional medicating applications, and is particularly valuable in use as a topical anesthetic device.
Historically, dermal anesthesia for minor skin surgery has been achieved by the local infiltration of anesthetic solution via a needle and syringe. Although this technique is effective, it suffers from several drawbacks. Many patients, especially children, do not tolerate the pain of an injection well. Injection of a fluid into infected tissue can result in spread of the infecting organism(s) along the needle track. Additionally, injection of a bolus of local anesthetic into an allergic patient could result in a more severe reaction than a topically applied drug.
Generally speaking, local anesthetics do not penetrate into the skin in sufficient concentration to provide surgical anesthesia. In recent years, creams containing a Eutectic Mixture of Local Anesthetics (EMLA) such as lidocaine and prilocaine have been found useful as a topical anesthetic for superficial skin procedures. The EMLA cream is applied to a lesion and adjacent tissue and covered with an occlusive dressing for about 20 minutes to about 2 hours. More recently, a formulation of 30% lidocaine in an acid mantle cream has been found to be an effective and inexpensive topical anesthetic. While the EMLA and lidocaine creams are welcomed alternatives to anesthetic infiltration via injection, they have several drawbacks. For example, in the podiatric clinical setting, a cream applied to the foot and covered with an occlusive film would obviously smear when shoes were applied and the patient ambulated.
What is needed is a topical medicating device utilizing a viscoelastic gel pad having a liquid fraction wherein the medication is incorporated within the liquid fraction, where the viscoelastic gel pad is migration-controlled and the application of medication is limited to a specifically defined target skin surface. Such a topical drug delivery system is especially needed in the topical application of a local anesthetic.